Non-contacting gas compressor seal

ABSTRACT

A non-contacting gas compressor seal assembly is disclosed with an intermediate buffer chamber. The process gas is corrosive or otherwise hazardous and is contained from entering the atmosphere by pumping the barrier gas toward the process fluid. The inboard seal of the assembly is designed to maintain a sealing relationship in the event of loss of buffer gas pressure by operating as a non-contacting seal on the process fluid.

BACKGROUND OF THE INVENTION

[0001] Non-contacting seals are successfully employed in gas compressorsto provide a seal against loss of process gas. Such a seal is shown, forexample, in U.S. Pat. No. 4,212,475 to Sedy.

[0002] In practice, non-contacting seals are often arranged in anassembly having two spaced apart sets of relatively rotating ringswhich, in some applications, define an intermediate chamber containing apressurized barrier gas. The seal ring sets each include a mating ringand an axially movable primary ring. Grooves formed on the face of oneof the rings of each set communicate with the barrier gas. One seal setpumps gas from the buffer chamber toward the process fluid. The otherpumps toward the atmosphere. An example of such a seal is the doubleType 28 gas compressor seal manufactured by John Crane Inc., MortonGrove, Ill.

[0003] Gas compressor seals of the type described are configured suchthat on loss of buffer or barrier gas, the inboard seal opens anddefines a leakage path to the intermediate chamber. The outboard pair ofseal rings operates as a non-contacting seal and pumps a controlledamount of the process gas between the faces. However, since loss ofbuffer gas often results from failure of the outboard seal, opening ofthe faces of the inboard seal could cause undesirable leakage throughthe buffer chamber to atmosphere.

[0004] Non-contacting seals that operate on a film of gas have morerecently been employed to seal liquid in pump applications. An exampleis found in U.S. Pat. No. 5,375,853. There, spaced seal sets define abuffer chamber for gas at a pressure higher than the process. Theinboard seal set pumps the gaseous barrier across the relativelyrotatable faces toward the process fluid. The outboard set pumps thebarrier gas toward the atmosphere. John Crane Inc. manufactures andsells such a seal arrangement for pumps under the designation T-2800.

[0005] In pump applications, the inboard seal set is configured suchthat on loss of buffer pressure the inboard seal closes and operates asa contacting seal sufficiently long to permit shut-down of the pump.Such an arrangement would not be feasible in the gas compressorenvironment because the resulting face contact could affect structuralintegrity.

[0006] It has been determined, however, that in gas compressor andsimilar applications, the process fluid can effectively be containedupon a pressure reversal if the inboard seal ring set were arranged tocontinue to operate as a non-contacting seal with the process fluidproviding the requisite lift. In this way only a small, controlledquantity of process gas would pass to the buffer chamber, thereby,minimizing loss to atmosphere. The present invention is directed to aseal assembly arranged to provide this capability.

SUMMARY OF THE INVENTION

[0007] The present invention provides a non-contacting seal arrangementbetween a housing and relatively rotatable shaft to contain a processfluid in the housing which, on loss of barrier fluid pressure, theinboard seal continues to operate as a non-contacting seal. The sealarrangement includes a pair of spaced sets of relatively rotating ringsdefining an intermediate chamber to receive a barrier gas at a pressureexceeding process fluid pressure. Each set includes a non-rotatable ringand a rotatable ring, one of the rings being movable axially relative tothe other. Each ring of each set defines a generally radial annularsealing face in relatively rotating sealing relation to the sealing faceof the other ring of the set at a sealing interface. One of the rings ofat least one set has a pumping mechanism thereon arranged to pumpbarrier gas from the intermediate chamber between the interface. Thatset is adapted to be disposed to pump barrier gas toward the processfluid in the housing. The pumping mechanism of the ring is furtherconfigured to pump process fluid between the interface toward theintermediate chamber when the process fluid pressure exceeds thepressure of the barrier gas.

[0008] More particularly, the invention may include a retainer tosupport the axially movable ring of the set disposed to pump barrier gastoward the process fluid. The retainer and ring define an axiallyelongated annular pocket. An O-ring seal is disposed in the pocket andprovides a secondary seal between the retainer and the ring. It is sizedsuch that it has a cross-sectional diameter that is smaller than boththe axial and radial extent of the pocket.

[0009] The axially movable ring of the seal set disposed to pump barrierfluid toward the process may include a first portion defining theradially directed sealing face, a second portion supporting the ring foraxial movement, and an intermediate portion configured to decouple saidfirst and second portions to ensure a parallel relationship between therelatively rotating sealing faces under varying conditions of operatingpressure and temperature.

[0010] The invention further contemplates the method of sealing usingthe seal assembly comprising providing a barrier gas in the intermediatechamber at a pressure in excess of the pressure of said process fluid,pumping barrier gas from the intermediate chamber between the interfacetoward the process fluid when the pressure of the barrier gas exceedsthe pressure of the process fluid, and pumping process fluid between theinterface toward the intermediate chamber when the process fluidpressure exceeds the pressure of the barrier gas.

DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a cross-sectional elevational view of an embodiment of aseal assembly illustrative of the present invention.

[0012]FIG. 2 is a fragmentary plan view of the mating ring face of theoutboard seal set of the apparatus of FIG. 1.

[0013]FIG. 3 is a fragmentary plan view of the mating ring face of theinboard seal set of the apparatus of FIG. 1.

[0014]FIG. 4 is a sectional view of the inboard seal set of theapparatus of FIG. 1, showing a different operational mode.

[0015]FIG. 5 is an elevational view, in section, of a preferred form ofthe primary ring of the inboard seal of the apparatus of FIG. 1.

DETAILED DESCRIPTION

[0016]FIG. 1 illustrates a dual, non-contacting seal assembly generallydesignated 10 illustrative of the principles of the present invention.It is operatively positioned between a housing 12 of a piece ofturbomachinery equipment such as a gas compressor and its rotatableshaft 16. Housing 16 defines an inner chamber 18 containing processfluid pressurized by the operation of the compressor. The seal assembly10 contains the gas from passage between the shaft 16 and housing 12 tothe surrounding environment.

[0017] The embodiment shown is illustrative of the principles of theinvention, but is not to be considered limiting. The invention could beapplied to seal assemblies having, for example, rotating seal heads. Itis further contemplated that the invention could be employed in a singlenon-contacting seal configuration or in an assembly including both anon-contacting and a contacting seal. Also, it is contemplated that theinvention could be employed to seal a process fluid such as a high vaporpressure liquid such as liquid propane or the like.

[0018] The seal assembly 10 is a dual seal arrangement comprised of aninboard seal ring set 22 adjacent the process gas chamber 18 and anoutboard seal ring set 24 adjacent the ambient environment external tohousing 12. The seal ring sets 22 and 24 define an intermediate bufferor barrier fluid chamber 26 that contains a buffer gas such as nitrogen,which is inert to the process gas. The barrier gas is normallymaintained at a pressure exceeding the process gas pressure. Chamber 26is defined by liner 28 which is fixed to housing 12 and attaches thenon-rotating elements of the seal assembly to the housing 12. Sleeveassembly 32 surrounds shaft 16 and secures the rotating components tothe shaft.

[0019] Outboard seal ring set 24 includes a rotating seal ring 36 and astationary seal ring 38. Ring 38 is axially movable to accommodate axialtranslation of the shaft 16 and associated sleeve 32 during compressoroperation. Such movement could be as much as one-sixteenth of an inch ormore in either axial direction from the nominal position.

[0020] Seal ring 36 defines an annular generally radial seal face 40 inrelatively rotatable sealing relation with an annular, generally radialsealing face 42 of ring 38.

[0021] Rotating sealing ring 36, referred to as the mating ring, issecured to sleeve 32 by collar 44. It is axially fixed relative to theshaft 16. An O-ring 45 provides a secondary seal between a back face ofring 36 and an adjacent radial surface formed on radial extension 43 ofsleeve 32.

[0022] Face 40 of mating ring 36 includes a pattern of depressions andlands forming a pumping mechanism to pump barrier fluid from chamber 26between the faces toward the surrounding environment. A preferredpumping mechanism is a series of spiral grooves 46 best seen in FIG. 2.These grooves and lands commence at the radially outer circumferentialedge of the interface between the faces 40-42 and are open to thechamber 26. They extend toward an ungrooved area or dam 48 adjacent theradially inner circumferential edge of the interface. During operation,pumping of the barrier gas between the interface 40-42 creates lift toseparate these faces for non-contacting performance.

[0023] Seal ring 38, usually referred to as the primary ring, includesan inner cylindrical surface 50. It also has a series of drive groovesabout its outer periphery and has a radial back face 52.

[0024] Seal ring 38 is supported on a retainer 54, which is fixed tohousing liner 28. Ring 38 defines an outer cylindrical surface 56 of adiameter slightly smaller than inner cylindrical surface 50 of ring 38.This relationship permits axial translation of ring 38.

[0025] The ring 38 is held against rotation by interengagement of one ormore drive lugs 57 on retainer 54 with the drive grooves formed aboutouter diameter of ring 38. This relationship is such as to precluderotation of ring 38 but permit axial movement.

[0026] A series of axially directed compression coil springs 58 arepositioned in pockets 60 formed in retainer 54. A spring disc 62 isdisposed between springs 58 and rear face 52 of the primary ring 38. Thedisc 58 receives the axial force imparted by the springs 58, to urge ittoward the rear face 52 of the primary ring 38.

[0027] Disc 62 forms a pocket adjacent rear face 52 of primary ring 38.The pocket includes an axial surface 66 and a radial surface 67 whichdefine an O-ring receptacle. O-ring 68 is disposed in the pocket. It iscompressed between radial surface 67 of disc 62 and back radial face 52of the primary ring 38. It provides a secondary seal to preclude passageof gas between the back of ring 38 and disc 62. The O-ring 68 is sizedto contact outer cylindrical surface 56 of retainer 54 but permit axialmovement of the primary ring 38, disc 62 and O-ring 68 to accommodateaxial translation of shaft 16 relative to housing 12.

[0028] Inboard seal ring set 22 includes a rotating seal ring 136 and astationary seal ring 138. Ring 138 is axially movable to accommodateaxial translation of shaft 16 and associated sleeve 32.

[0029] Seal ring 136 defines an annular, generally radial seal face 140in relatively rotatable sealing relation with annular, generally radialsealing face 142 of ring 138.

[0030] Rotating sealing ring 136 is secured to sleeve 32 by collar 144.It is axially fixed relative to the shaft 16. An O-ring 145 provides asecondary seal between a back face of ring 136 and an adjacent radialsurface formed on radial extension 43 of sleeve 32.

[0031] Face 140 of mating ring 136 includes a pattern of depressions andlands forming a pumping mechanism to pump barrier fluid from chamber 26between the faces toward the process gas. Best seen in FIG. 3, thepreferred pumping mechanism is a radially outer pattern of spaced spiralgrooves 146 and associated lands 147. The grooves are open to thechamber 26 and extend radially inward toward an ungrooved area or dam148. During operation, pumping of the barrier gas between the interface140-142 to process chamber 18 creates the requisite lift to separatethese faces for non-contacting performance.

[0032] Referring to FIG. 3, for clarity the radial extent and positionof the interface between face 140 of mating ring 136 and face 142 ofprimary ring 138 is illustrated by dashed lines. The groove and landpattern 146-147 commences at the outer circumferential periphery ofmating ring 136 and extends inwardly toward the process chamber 18. Thepattern terminates short of the inner circumferential periphery of theinterface 140-142 to define dam 148.

[0033] The face pattern of grooves described above with respect to themating ring 136 of inboard seal ring set 22 is commonly used in gascompressor seals such as the T-28 double seal manufactured by John CraneInc. The pattern of the grooves 46 and lands 47 on the face 40 of matingring 36 of outboard seal ring set 24 would be essentially the samespiral groove and land pattern. However, the angle of spiral is in theopposite direction of that formed on ring 136.

[0034] In accordance with the present invention, the pumping mechanismformed on radial face 140 of mating ring 136 includes a pattern ofradially inner spiral grooves 149 separated by associated ungroovedlands 143. These grooves communicate with the process fluid in chamber18 and extend radially outwardly from the inner circumferentialperiphery of interface 140-142 toward the radial inward terminus ofspiral grooves 146. The grooves 149 terminate short of the radiallyinner terminus of grooves 146. The land between these groove patternsdefines a continuous ungrooved annular dam 148.

[0035] The spiral grooves 149 are angled oppositely from the grooves146. They, therefore, are arranged to pump from the process chamber 18toward the intermediate or barrier gas chamber 26. The grooves 146 andlands 147 are equal in circumferential extent. The grooves 149 have acircumferential extent of one half the circumferential extent of eachassociated land. The spiral grooves 146 and associated lands 147 spanabout 55-60% of the radial extent of the interface 140-142, preferablyabout 58%. The spiral grooves 149 and associated lands 143 span about 10to 15%, preferably about 13%, of the radial extent of the interface. Theintermediate dam spans the remainder.

[0036] The grooves 149 are also shallower than the grooves 146. Grooves146 have a depth of about 0.0005 inches. Grooves 149 have a depth ofabout 0.0002 inches. The grooves are at an angle of 15° to a tangent tothe circumference from which they extend. The radially inner tip of eachgroove 149 is aligned on a radial line with the radially inner tip ofevery other groove 146.

[0037] Seal ring 138 is axially elongated as compared to seal ring 38 ofoutboard seal set 24. It includes a first inner cylindrical surface 150and a second inner cylindrical surface 151 which is of a diametersmaller than first inner cylindrical surface 150. A radial sealingsurface 153 extends from second inner cylindrical surface 151 and joinsfirst inner cylindrical surface 150 with a radius or fillet. Ring 138also has a series of drive grooves about its outer periphery and aradial back face 152.

[0038] Primary ring 138 is a unitary component made from a single blankof material. As best understood with reference to FIG. 5, ring 138 isconfigured to decouple an outboard end portion 138 a, which definesradial face 142 from an inboard end portion 138 c which supports thering in the assembly 10. An intermediate portion 138 b connects the endportions 138 a and 138 c. This configuration permits the radial faces140 and 142 to remain essentially parallel over the range of pressuresand temperatures experienced during operation.

[0039] Seal ring 138 is supported on a retainer 154 fixed to housing 12by liner 28. Retainer 154 defines a first outer cylindrical surface 155supporting surface 150. It is of a diameter slightly smaller than thefirst inner cylindrical surface 150. Retainer 154 includes a secondouter cylindrical surface 156 supporting surface 151 of ring 138. It isof a diameter smaller than the second inner cylindrical surface 151 ofring 138. This relationship permits axial translation of ring 138relative to retainer 154.

[0040] A radial sealing surface 159 extends radially inwardly from firstouter cylindrical surface 155 and joins second outer cylindrical surface156 at axially extending conical ramp 161. Ramp 161 extends radiallyoutwardly at a 20° angle to the horizontal from its intersection withsecond outer cylindrical surface 156 to its joinder with radial sealingsurface 159.

[0041] The ring 138 is held against rotation by interengagement of oneor more drive lugs 157 on retainer 154 with drive grooves formed aboutouter diameter of ring 138. This relationship is such as to precluderotation of ring 138 but permit axial movement.

[0042] A series of axially directed compression coil springs 158 arepositioned in pockets 160 formed in retainer 154. A spring disc 162 isdisposed between springs 158 and rear face 152 of the primary ring 138.The disc 162 receives the axial force imparted by the springs 158 andtransfers it to a rear face 152 of primary ring 138.

[0043] A secondary seal in the form of an O-ring 168 prevents passage ofgas between retainer 154 and primary ring 138. The first innercylindrical surface 150 of primary ring 138, and radial sealing surface153 of primary ring 138, second outer cylindrical surface 156 ofretainer 154, conical ramp 161 and radial sealing surface 159 ofretainer 154 define an axially elongate annular O-ring pocketsurrounding secondary seal O-ring 168. The pocket has an axial extentbetween radial sealing surface 153 of ring 138 and radial sealingsurface 159 of retainer 154 that exceeds the cross-sectional diameter ofthe O-ring. The ring 168 is, therefore, free to move axially within thepocket as the shaft 16 translates axially relative to housing 12. Firstinner cylindrical surface 150 of ring 138 overlies second outercylindrical surface 156 of retainer 154. These surfaces define theradial extent of the annular pocket.

[0044] O-ring 168 is sized to define an inner peripheral surface thatslightly contacts second outer cylindrical surface 156 of retainer 154.As illustrated in FIG. 1, at ambient design temperature of 70° F.(Fahrenheit), it has cross-sectional diameter such that the outerperipheral surface is slightly spaced from first inner cylindricalsurface 150 of primary ring 138. This relationship of thecross-sectional diameter of the O-ring 168 to the radial extent of theO-ring seal pocket results from the need to accommodate axialtranslation of the primary ring 138 under all conditions of elevatedoperating temperature.

[0045] Complication arises from the different rates of thermal expansionof the materials used in the various seal components. Typically, themating rings 36 and 136 are silicon carbide or tungsten carbide. Theprimary rings 38 and 138 are carbon. The secondary seal O-rings 68 and168 and other O-ring seals are a polymeric material such as Kalrez, afluoroelastomer manufactured by E. I. duPont & Company. Otherfluoroelastomers could be used, depending on compressor operatingtemperatures. The remaining metal parts, such as retainers 54 and 154,are stainless steel, such as 410 stainless or Hastelloy C.

[0046] Operating temperatures range from ambient, which, for designpurposes, is 70° F. to operating, which could be in the range of 300° F.to 350° F. or higher. At operating temperatures, about 325° F., theradial extent of the O-ring pocket is smaller than it is at ambient orother temperatures below operating. A cross-section of O-ring 168, sizedto fit the largest radial extent, would experience excessive radial loadat operating temperature. Hence, it is necessary to size the O-ring 18to accommodate all conditions of operation.

[0047] In this instance the O-ring 168 is configured for ambienttemperature of 70° F. to define an internal circumference sufficient toexpand slightly onto the second outer circumferential surface 156 ofretainer 154. To avoid excessive radial compression within the pocket atoperating temperature, 325° F., the diameter of the cross-section of theO-ring 168 is smaller at ambient temperature of 70° F. than the radialdistance between first inner cylindrical surface 150 of primary ring 138and second outer cylindrical surface 156 of retainer 154. As a result,on pressure reversal at ambient temperature, an effective secondary sealbetween the primary ring 138 and retainer 154 could not be assured.Conical ramp 161 on second outer cylindrical surface 156 of retainer 154solves this problem.

[0048] In operation, barrier gas in chamber 26 is maintained at apressure that exceeds the process pressure generated by the compressoroperation. Shaft 16 and sleeve 32 rotate at operating speed rotatingmating rings 36 and 136. The pumping mechanisms on the faces 40 and 140,in particular the spiral grooves exposed at the radial outer peripheryof the interface of faces 40-42 and 140-142, pump barrier gas betweenthe seal faces causing lift and resulting in non-contacting operation.

[0049] In the event of a loss of barrier gas pressure, the processpressure in chamber 18 exceeds the pressure in the barrier chamber 26.Because the radially inner spiral grooves 149 are exposed to the processgas and the inner periphery of the seal ring interface 140-142, processgas is pumped between the faces to provide lift and permit continuednon-contacting operation of the inner seal ring set 22.

[0050] Secondary O-ring seals 45 and 68 in outboard seal ring set 24separate the barrier gas chamber 26 from the surrounding environment 20.Secondary seals 145 and 168 in inboard seal ring set 22 separate thebarrier gas chamber 26 from the process gas chamber 18.

[0051] In normal operation conditions, the barrier gas is at a pressurethat exceeds the process gas pressure. The O-ring 168 is, therefore,urged toward radial sealing surface 153 in the O-ring seal pocket andseats against the radial sealing surface 153 of primary ring 138 and thesecond outer cylindrical surface 156 of retainer 154.

[0052] As illustrated in FIG. 4, a pressure reversal causes the O-ring168 to be urged axially toward radial sealing surface 159 of retainer154. To effect a sealing relationship, it is necessary that the O-ring168 engage both the radial sealing surface 159 of retainer 154 and firstinner cylindrical surface 150 of primary ring 138. At certain operatingconditions, for example, ambient temperature of 70° F., the size of theouter circumference of O-ring 168 and the radial distance between secondouter cylindrical surface 156 of retainer 154 and first innercylindrical surface 150 of primary ring 138 are such that sealingengagement with first inner cylindrical surface 150 would not occur.Inclined conical ramp 161, however, causes the inner circumference ofO-ring 168 to expand radially as the ring moves toward radial sealingsurface 159 of retainer 154.

[0053] Process pressure, acting on O-ring 168, causes it to travelaxially from second outer cylindrical surface 156 of retainer 154 to aposition overlapping inclined conical ramp 161 where it is also pressedagainst radial sealing surface 159. The conical ramp causes the innercircumference of O-ring 168 to expand sufficiently to ensure sealingengagement of the outer circumferential periphery of the O-ring 168 withsecond inner cylindrical surface 150 of primary ring 138. The O-ring 168also contacts the radial surface 159 of retainer 154 in sealingrelation. Thus, even at ambient design temperature of 70° F., aneffective secondary seal is accomplished which continues to separate theprocess chamber 18 from the barrier gas chamber 26.

[0054] Seal balance ratio is the ratio of the amount of force from fluidpressure acting on the back of the axially movable seal ring tending toclose the faces divided by the forces between the faces tending to openthem. It is measured by the ratio of areas exposed to such pressurecausing such closing and opening forces.

[0055] It should be noted that in the seal of FIG. 1 the inboard sealset is configured to change the balance on pressure reversal, therebymaintaining a sufficient balance to ensure that the faces 140-142 remainin an operational relationship.

[0056] In this regard, under normal operation, the barrier gas pressureexceeds the process. O-ring 168 is seated against second outercylindrical surface 156 which determines the area of back face 152 ofprimary ring 138 exposed to pressure in the barrier chamber 26. Thecircumference of second outer cylindrical surface 156 is the balancediameter.

[0057] On a pressure reversal, O-ring 168 is urged against radialsealing surface 159 and first inner cylindrical surface 150 of primaryring 138. The balance diameter shifts to the circumference of firstinner cylindrical surface 150 with those radial surfaces of primary ring138 radially inward of the circumference representing the area subjectedto the higher pressure of the process fluid. With such a shift inbalance diameter, balance may be maintained at levels in excess of 0.5regardless of the location of higher pressure.

[0058] Balance under normal conditions of a barrier gas pressure inexcess of process pressure can be about 0.85. On reversal conditions,with the process pressure higher than the pressure in the barrier gaschamber 28, a balance can be about 0.65. It should be noted that balancein either direction can be increased by decreasing the diameter of theouter circumferential periphery of the interface 140-142 of rings136-138.

[0059] The reverse pumping grooves 149 produce lift that counteracts theclosing force and avoids damage to primary ring 138 and mating ring 136due to hard contact on a pressure reversal. The grooves are sized toproduce lift such that, on pressure reversal, the faces 140 and 142operate with no contact or slight contact. Hard contact due to pressurereversal is avoided.

[0060] As previously explained, the primary ring 138 of inboard seal set22 is axially elongated with that portion 138 a defining the radialsealing face 142 decoupled from that portion 138 c supported on retainer154. The intermediate portion 138 b defines a flexible transition.

[0061]FIG. 5 shows a cross-section of primary ring 438 illustrative of apreferred configuration for primary ring 138. It is a unitary ring madeof a single blank of carbon material.

[0062] Ring 438 includes portion 438 a that defines a radial sealingface 442 for relatively rotating sealing relation with a sealing face140 of a mating ring 136. Axial extent of portion 438 a between face 442and a back wall 467 is about 17% of the total axial extent of the ring.It includes inner cylindrical surface 454 of a diameter smaller thansecond outer cylindrical surface 156 of retainer 154. It also includesan outer cylindrical surface 455.

[0063] Portion 438 c defines first inner cylindrical surface 450 adaptedto be supported on first outer cylindrical surface 155 of retainer 154.It includes outer cylindrical surface 457 having drive notches forengagement with lugs 157 of retainer 154. Axially, portion 438 c extendsabout the same distance as the distance between back face 452 and radialsealing surface 453. It represents about 24% of the axial extent of thering 438.

[0064] Radial sealing surface 453 extends radially outward from a secondinner cylindrical surface 451 and connects to first inner cylindricalsurface 450 by a fillet or radius. Second inner cylindrical surface 451is adapted to be supported for axial translational movement on secondouter cylindrical surface 156 of retainer 154 shown in FIG. 1. Firstinner cylindrical surface 450 is adapted to define an O-ring pocket withradial sealing surface 453, second outer cylindrical surface 156 ofretainer 154 and a radial sealing surface 159 on the retainer such asillustrated in FIG. 1.

[0065] The axial outer portions 438 a and 438 c are connected byintermediate portion 438 b which provides the flexibility necessary tostructurally decouple the end portions. Intermediate portion 438 b isabout 40% of the axial extent of ring 438. It is comprised of twoportions 438 b(1) adjacent portion 438 c.

[0066] Portion 438 b(2) comprises about 20% of the axial length of ring438. It is defined by the inner cylindrical surface 451 which is adaptedto be supported on second outer cylindrical surface 156 of retainer 154and the radial sealing, surface 453. The diameter of second innercylindrical surface 451 is larger than the diameter of inner cylindricalsurface 454 of portion 438 a. Portion 438 b(2) includes an outercylindrical surface 459 which is of a diameter smaller than the diameterof outer cylindrical surface 455 of portion 438 a.

[0067] Portion 438 b(1) is the most flexible portion of ring 438. Itcomprises about 40% of the axial extent of the ring 438. It includes aninner cylindrical surface 461 having a diameter equal to the diameter ofinner cylindrical surface 454 of portion 438 a. The outer surface ofportion 438 b(1) is of a compound shape. It includes a conical surface463 that extends from portion 438 b(2) commencing at a diameter aboutequal to that of first inner cylindrical surface 450 at an angleradially inwardly of 11° to the horizontal to a semi-circular groove 465formed adjacent commencement of portion 438 a. The radius of the grooveis about 4% of the axial extent of ring 454.

[0068] The radial extent of the various portions of ring 438 referenceto the radial extent of portion 438 a are as follows. The radial extentof portion 438 c relative to the radial extent of portion 438 a is 70%.The radial extent of portion 438 b(2) relative to portion 438 a is 66%.The radial extent of the portion 438 b(1) at the groove 465 relative tothe radial extent of portion 438 a is 28%.

[0069] The ring 438 described above provides the strength necessary tooperate at the pressures and temperatures experienced in the compressorenvironment and the flexibility to ensure that the surfaces of therelatively rotating faces of the inboard seal set remain parallel overthe operating range. The portions 438 a and 438 c have relatively largemass to withstand these operational conditions. Portion 438 b providesthe requisite flexibility to the structure.

[0070] Seals have been manufactured incorporating the present invention.Two sizes have been made; for a 7.625 inch shaft and a 5.250 inch shaft.

[0071] For the 7.625 inch shaft size, the primary ring portion 438 adefining the relatively rotatable sealing face 442 had an outer diameterof 8.572 inches. The seal ring interface 140-142 had an axial extent of0.414 inches commencing at an outer circumferential diameter of 4.340inches. Outer cylindrical surface 457 had a diameter of 8.852 inches.The surface 454 was 7.446 inches in diameter. The overall axial lengthof ring 454 was 1.250 inches. First inner cylindrical surface 450 had adiameter of 8.052 inches. Second inner cylindrical surface 451 had adiameter of 7.651 inches.

[0072] These seals were designed to experience a maximum processpressure of 200 psig (pounds per square inch gauge). The barrier gaspressure employed was 250 psig.

[0073] The O-ring 168 for the 7.625 inch seal had a cross-section of0.205 to 0.215 inches. It had an inside circumferential diameter of7.430 to 7.520 inches.

[0074] First outer cylindrical surface 155 had a diameter of 7.993inches. The second outer cylindrical surface 156 had a diameter of 7.627inches and a length of 0.513 inches including a 0.093 inch by 30°chamfer. The conical ramp 161 was 0.100 inches in axial extent.

[0075] Various features of the invention have been described inconnection with the illustrated embodiment of the invention. Variousmodifications may be made without departing from the scope of theinvention.

We claim:
 1. A non-contacting seal assembly to seal between a housingcontaining a process fluid and a relatively rotating shaft, saidassembly comprising a pair of spaced sets of relatively rotating ringsdefining an intermediate chamber to receive a barrier gas at a pressureexceeding process fluid pressure; each said set including anon-rotatable ring and a rotatable ring, one of said rings beingmoveable axially relative to the other, each ring of each set defining agenerally radial annular sealing face in relatively rotating sealingrelation to the sealing face of the other ring of said set at a sealinginterface; one of said rings of at least one set having a pumpingmechanism thereon arranged to pump barrier gas from said intermediatechamber between said interface; said one of said sets adapted to bedisposed to pump barrier gas toward the process fluid, said setincluding a retainer to support said axially moveable ring for axialtranslation thereon, said retainer and said ring defining an axiallyelongated annular pocket therebetween; an O-ring seal disposed in saidpocket; said O-ring being sized such that it has a cross-sectionaldiameter that is smaller than both the axial and radial extent of thepocket, said O-ring providing a secondary seal between said axiallymoveable ring and said retainer.
 2. A non-contacting seal assembly asclaimed in claim 1, wherein said retainer includes an outer cylindricalsealing surface forming part of said pocket and supporting said O-ringthereon and a radial sealing surface forming an axial end of saidpocket, said retainer further including a conical ramp extendingradially outward between said cylindrical sealing surface and saidradial sealing surface, said O-ring being moveable from a position onsaid cylindrical sealing surface of said retainer to a position on saidconical ramp in sealing contact with said radial sealing surface of saidretainer.
 3. A non-contacting seal assembly as claimed in claim 2wherein said ring supported on said retainer includes an innercylindrical sealing surface overlying said outer cylindrical sealingsurface of said retainer and defining a part of said annular pocket,said ring further includes a radial sealing surface spaced from saidradial sealing surface of said retainer to further define said annularpocket, said O-ring being positionable in sealing contact with saidradial sealing surface of said ring when positioned on said outercylindrical sealing surface of said retainer and being positionable insealing contact with said inner cylindrical surface of said ring whenpositioned on said conical ramp in sealing relation to said radialsealing surface of said retainer.
 4. A non-contacting seal assembly asclaimed in claim 1 wherein said O-ring has a cross sectional diameterthat is smaller than the radial extent of the pocket, an ambient designtemperature of 70 degrees F., and, wherein, the inner peripheral surfaceof said O-ring is in contact with said outer cylindrical sealing surfaceof said retainer at said design temperature.
 5. A non-contacting sealassembly as claimed in claim 2 wherein said O-ring is in contact withsaid outer cylindrical sealing surface of said retainer when the barriergas pressure exceeds the pressure of the process fluid.
 6. Anon-contacting seal assembly as claimed in claim 3 wherein said O-ringis in contact with said outer cylindrical sealing surface of saidretainer and said radial sealing surface of said ring when the barriergas pressure exceeds the pressure of the process.
 7. A non-contactingseal assembly as claimed in claim 4 wherein said O-ring is in contactwith said outer cylindrical sealing surface of said retainer and saidradial sealing surface of said ring when the barrier gas pressureexceeds the pressure of the process.
 8. A non-contacting seal assemblyas claimed in claim 2 wherein said O-ring overlies said conical ramp incontact with said radial sealing surface of said retainer when thepressure of the process fluid exceeds the pressure in the intermediatechamber.
 9. A non-contacting seal assembly as claimed in claim 3 whereinsaid O-ring overlies said conical ramp in contact with said radialsealing surface of said retainer and said cylindrical sealing surface ofsaid ring when the pressure of the process fluid exceeds the pressure inthe intermediate chamber.
 10. A non-contacting seal assembly as claimedin claim 4 wherein said O-ring overlies said conical ramp in contactwith said radial sealing surface of said retainer and said cylindricalsealing surface of said ring when the pressure of the process fluidexceeds the pressure in the intermediate chamber.
 11. A non-contactingseal assembly as claimed in claim 5 wherein said O-ring overlies saidconical ramp in contact with said radial sealing surface of saidretainer and said cylindrical sealing surface of said ring when thepressure of the process fluid exceeds the pressure in the intermediatechamber.
 12. A non-contacting seal assembly as claimed in claim 6wherein said O-ring overlies said conical ramp in contact with saidradial sealing surface of said retainer and said cylindrical sealingsurface of said ring when the pressure of the process fluid exceeds thepressure in the intermediate chamber.
 13. A non-contacting seal assemblyas claimed in claim 7 wherein said O-ring overlies said conical ramp incontact with said radial sealing surface of said retainer and saidcylindrical sealing surface of said ring when the pressure of theprocess fluid exceeds the pressure in the intermediate chamber.
 14. Anon-contacting seal assembly as claimed in claim 1 wherein the pumpingmechanism includes a pattern of spiral grooves and lands formed on theradial sealing face of said one ring of said set, said grooves are opento the intermediate chamber at one circumferential periphery of theinterface between the relatively rotating sealing faces of said set, andterminate at an ungrooved area defining a sealing dam.
 15. Anon-contacting seal assembly as claimed in claim 14 wherein the pumpingmechanism on the face of said one of said rings of said set includes apattern of oppositely directed spiral grooves and lands adapted forcommunication with the process fluid at the other circumferentialperiphery of said interface to pump in a direction opposite the patternof spiral grooves open to said intermediate chamber.
 16. Anon-contacting seal assembly as claimed in claim 15 wherein saidoppositely directed pattern of grooves and lands include one groove forevery other groove of said pattern open to said intermediate chamber.17. A non-contacting seal assembly as claimed in claim 16 wherein saidpattern of oppositely directed grooves has a radial extent that is lessthan the radial extent of the pattern of spiral grooves open to saidintermediate chamber, said patterns defining an ungrooved dam betweenthem.
 18. A non-contacting seal assembly as claimed in claim 17 whereinthe depth of the grooves of said reverse pumping grooves is less thanthe depth of said grooves open to said intermediate chamber.
 19. Anon-contacting seal assembly as claimed in claim 18 wherein said reversepumping grooves are one half of the circumferential extent of theassociated land and the grooves open to said intermediate chamber areequal in circumferential extent to the associated land.
 20. Anon-contacting seal assembly as claimed in claim 19 wherein said reversepumping grooves have a radial extent that is about 21 to 24% of theradial extent of said interface between said relatively rotating sealingfaces and said grooves open to said intermediate chamber span about 55to 60% of the radial extent of said interface.
 21. A non-contacting sealassembly as claimed in claim 1 wherein said axially moveable ring ofsaid set adapted to pump barrier gas toward the process fluid includes afirst portion defining said radially directed sealing face, a secondportion supporting said ring for axial movement, and an intermediateportion configured to decouple said first and second portions to ensurea parallel relationship between said relatively rotating sealing facesunder varying conditions of operating pressure and temperature.
 22. Anon-contacting seal assembly as claimed in claim 21 wherein saidintermediate portion includes a portion having a radial extent that isless than the radial extent of said first and second portions.
 23. Anon-contacting seal assembly as claimed in claim 22 wherein saidintermediate portion defines an annular groove adjacent said firstportion to provide said flexibility of said intermediate portion todecouple said first and second portions.
 24. A non-contacting sealassembly to seal between a housing containing a process fluid and arelatively rotating shaft, said assembly comprising a pair of spacedsets of relatively rotating rings defining an intermediate chamber toreceive a barrier gas at a pressure exceeding process fluid pressure;each said set including a non-rotatable ring and a rotatable ring, oneof said rings being moveable axially relative to the other, each ring ofeach set defining a generally radial annular sealing face in relativelyrotating sealing relation to the sealing face of the other ring of saidset at a sealing interface; one of said rings of at least one set havinga pumping mechanism thereon arranged to pump barrier gas from saidintermediate chamber between said interface when the pressure of thebarrier gas exceeds the pressure of the process fluid; said one of saidsets adapted to be disposed to pump barrier gas toward the process fluidin the housing, wherein the pumping mechanism of said ring of said setis arranged to pump process fluid between said interface toward saidintermediate chamber when the process fluid pressure exceeds thepressure of the barrier gas.
 25. A non-contacting seal assembly asclaimed in claim 24, wherein said pumping mechanism includes a patternof spiral grooves and lands formed on the radial sealing face of saidone ring of said set, said grooves are open to the intermediate chamberat one circumferential periphery of the interface between the relativelyrotating sealing faces of said set, and terminate at an ungrooved areadefining a sealing dam.
 26. A non-contacting seal assembly as claimed inclaim 25 wherein the pumping mechanism on the face of said one of saidrings of said set includes a pattern of oppositely directed spiralgrooves and lands adapted for communication with the process at theother circumferential periphery of said interface to pump in a directionopposite the pattern of spiral grooves open to said intermediatechamber.
 27. A non-contacting seal assembly as claimed in claim 26wherein said oppositely directed pattern of grooves and lands includeone groove for every other groove of said pattern open to saidintermediate chamber.
 28. A non-contacting seal assembly as claimed inclaim 27 wherein said pattern of oppositely directed grooves has aradial extent that is less than the radial extent of the pattern ofspiral grooves open to said intermediate chamber, said patterns definingan ungrooved dam between them.
 29. A non-contacting seal assembly asclaimed in claim 28 wherein the depth of the grooves of said reversepumping grooves is less than the depth of said grooves open to saidintermediate chamber.
 30. A non-contacting seal assembly as claimed inclaim 29 wherein said reverse pumping grooves are one half of thecircumferential extent of the associated land and the grooves open tosaid intermediate chamber are equal in circumferential extent to theassociated land.
 31. A non-contacting seal assembly as claimed in claim30 wherein said reverse pumping grooves have a radial extent that isabout 21 to 24% of the radial extent of said interface between saidrelatively rotating sealing faces and said grooves open to saidintermediate chamber span about 55 to 60% of the radial extent of saidinterface.
 32. A non-contacting seal assembly as claimed in claim 24wherein said axially moveable ring of said set adapted to pump barriergas toward the process fluid includes a first portion defining saidradially directed sealing face, a second portion supporting said ringfor axial movement, and an intermediate portion configured to decouplesaid first and second portions to ensure a parallel relationship betweensaid relatively rotating sealing faces under varying conditions ofoperating pressure and temperature.
 33. A non-contacting seal assemblyas claimed in claim 32 wherein said intermediate portion includes aportion having a radial extent that is less than the radial extent ofsaid first and second portions.
 34. A non-contacting seal assembly asclaimed in claim 33 wherein said intermediate portion defines an annulargroove adjacent said first portion to provide said flexibility of saidintermediate portion to decouple said first and second portions.
 35. Anon-contacting seal assembly as claimed in claim 2 wherein the pumpingmechanism includes a pattern of spiral grooves and lands formed on theradial sealing face of said one ring of said set, said grooves are opento the intermediate chamber at one circumferential periphery of theinterface between the relatively rotating sealing faces of said set, andterminate at an ungrooved area defining a sealing dam.
 36. Anon-contacting seal assembly as claimed in claim 35 wherein the pumpingmechanism on the face of said one of said rings of said set includes apattern of oppositely directed spiral grooves and lands adapted forcommunication with the process at the other circumferential periphery ofsaid interface to pump in a direction opposite the pattern of spiralgrooves open to said intermediate chamber.
 37. A non-contacting sealassembly as claimed in claim 36 wherein said oppositely directed patternof grooves and lands include one groove for every other groove of saidpattern open to said intermediate chamber.
 38. A non-contacting sealassembly as claimed in claim 37 wherein said pattern of oppositelydirected grooves has a radial extent that is less than the radial extentof the pattern of spiral grooves open to said intermediate chamber, saidpatterns defining an ungrooved dam between them.
 39. A non-contactingseal assembly as claimed in claim 38 wherein the depth of the grooves ofsaid reverse pumping grooves is less than the depth of said grooves opento said intermediate chamber.
 40. A non-contacting seal assembly asclaimed in claim 39 wherein said reverse pumping grooves are one half ofthe circumferential extent of the associated land and the grooves opento said intermediate chamber are equal in circumferential extent to theassociated land.
 41. A non-contacting seal assembly as claimed in claim40 wherein said reverse pumping grooves have a radial extent that isabout 21 to 24% of the radial extent of said interface between saidrelatively rotating sealing faces and said grooves open to saidintermediate chamber span about 55 to 60% of the radial extent of saidinterface.
 42. A non-contacting seal assembly as claimed in claim 5wherein the pumping mechanism includes a pattern of spiral grooves andlands formed on the radial sealing face of said one ring of said set,said grooves are open to the intermediate chamber at one circumferentialperiphery of the interface between the relatively rotating sealing facesof said set, and terminate at an ungrooved area defining a sealing dam.43. A non-contacting seal assembly as claimed in claim 42 wherein thepumping mechanism on the face of said one of said rings of said setincludes a pattern of oppositely directed spiral grooves and landsadapted for communication with the process at the other circumferentialperiphery of said interface to pump in a direction opposite the patternof spiral grooves open to said intermediate chamber.
 44. Anon-contacting seal assembly as claimed in claim 43 wherein saidoppositely directed pattern of grooves and lands include one groove forevery other groove of said pattern open to said intermediate chamber.45. A non-contacting seal assembly as claimed in claim 44 wherein saidpattern of oppositely directed grooves has a radial extent that is lessthan the radial extent of the pattern of spiral grooves open to saidintermediate chamber, said patterns defining an ungrooved dam betweenthem.
 46. A non-contacting seal assembly as claimed in claim 45 whereinthe depth of the grooves of said reverse pumping grooves is less thanthe depth of said grooves open to said intermediate chamber.
 47. Anon-contacting seal assembly as claimed in claim 46 wherein said reversepumping grooves are one half of the circumferential extent of theassociated land and the grooves open to said intermediate chamber areequal in circumferential extent to the associated land.
 48. Anon-contacting seal assembly as claimed in claim 47 wherein said reversepumping grooves have a radial extent that is about 21 to 24% of theradial extent of said interface between said relatively rotating sealingfaces and said grooves open to said intermediate chamber span about 55to 60% of the radial extent of said interface.
 49. A non-contacting sealassembly as claimed in claim 11 wherein the pumping mechanism includes apattern of spiral grooves and lands formed on the radial sealing face ofsaid one ring of said set, said grooves are open to the intermediatechamber at one circumferential periphery of the interface between therelatively rotating sealing faces of said set, and terminate at anungrooved area defining a sealing dam.
 50. A non-contacting sealassembly as claimed in claim 49 wherein the pumping mechanism on theface of said one of said rings of said set includes a pattern ofoppositely directed spiral grooves and lands adapted for communicationwith the process at the other circumferential periphery of saidinterface to pump in a direction opposite the pattern of spiral groovesopen to said intermediate chamber.
 51. A non-contacting seal assembly asclaimed in claim 50 wherein said oppositely directed pattern of groovesand lands include one groove for every other groove of said pattern opento said intermediate chamber.
 52. A non-contacting seal assembly asclaimed in claim 51 wherein said pattern of oppositely directed grooveshas a radial extent that is less than the radial extent of the patternof spiral grooves open to said intermediate chamber, said patternsdefining an ungrooved dam between them.
 53. A non-contacting sealassembly as claimed in claim 52 wherein the depth of the grooves of saidreverse pumping grooves is less than the depth of said grooves open tosaid intermediate chamber.
 54. A non-contacting seal assembly as claimedin claim 53 wherein said reverse pumping grooves are one half of thecircumferential extent of the associated land and the grooves open tosaid intermediate chamber are equal in circumferential extent to theassociated land.
 55. A non-contacting seal assembly as claimed in claim54 wherein said reverse pumping grooves have a radial extent that isabout 21 to 24% of the radial extent of said interface between saidrelatively rotating sealing faces and said grooves open to saidintermediate chamber span about 55 to 60% of the radial extent of saidinterface.
 56. A method of sealing between a housing containing aprocess fluid and a relatively rotating shaft utilizing a non-contactingseal assembly comprising a pair of spaced sets of relatively rotatingrings defining an intermediate chamber to receive a barrier gas at apressure exceeding process fluid pressure; each said set including anon-rotatable ring and a rotatable ring, one of said rings beingmoveable axially relative to the other, each ring of each set defining agenerally radial annular sealing face in relatively rotating sealingrelation to the sealing face of the other ring of said set at a sealinginterface; one of said rings of at least one set having a pumpingmechanism thereon and disposed between said interface to pump barriergas toward the process fluid in the housing, the steps comprising:providing a barrier gas in said intermediate chamber at a pressure inexcess of the pressure of said process fluid, pumping barrier gas fromsaid intermediate chamber between said interface when the pressure ofthe barrier gas exceeds the pressure of the process fluid; pumpingprocess fluid between said interface of said seal set when the processfluid pressure exceeds the pressure of the barrier gas.
 57. A method ofsealing as claimed in claim 56 wherein said pumping mechanism includes apattern of spiral grooves and lands formed on the radial sealing face ofsaid one ring of said set, said grooves are open to the intermediatechamber at one circumferential periphery of the interface between therelatively rotating sealing faces of said set, and terminate at anungrooved area defining a sealing dam; and wherein the pumping mechanismon the face of said one of said rings of said set disposed to pumpbarrier gas toward the process fluid in the housing includes a patternof oppositely directed spiral grooves and lands adapted forcommunication with the process fluid at the other circumferentialperiphery of said interface to pump in a direction opposite the patternof spiral grooves open to said intermediate chamber, the steps furthercomprising utilizing said grooves to respectively pump said barrier gasand said process fluid.
 58. A method of sealing as claimed in claim 57wherein said set disposed to pump barrier gas toward said process fluidincludes a retainer to support said axially moveable ring for axialtranslation thereon, said retainer and said ring defining an axiallyelongated annular pocket therebetween; an O-ring seal disposed in saidpocket; said O-ring being sized such that it has a cross-sectionaldiameter that is smaller than both the axial and radial extent of thepocket; the steps further comprising providing a secondary seal betweensaid axially moveable ring and said retainer utilizing said O-ring. 59.A method of sealing as claimed in claim 58 wherein said retainerincludes an outer cylindrical sealing surface forming part of saidpocket and supporting said O-ring thereon and a radial sealing surfaceforming an axial end of said pocket, said retainer further including aconical ramp extending radially outward between said cylindrical sealingsurface and said radial sealing surface, said O-ring being moveable froma position on said cylindrical sealing surface of said retainer to aposition on said conical ramp in sealing contact with said radialsealing surface of said retainer; the steps further comprising providingsaid secondary seal with said O-ring on said outer cylindrical surfacewhen said barrier gas pressure exceeds the pressure of said processfluid, and providing said secondary seal with said O-ring on saidconical ramp when said process fluid pressure exceeds the pressure insaid intermediate chamber.
 60. A method of sealing as claimed in claim59 wherein said ring supported on said retainer includes an innercylindrical sealing surface overlying said outer cylindrical sealingsurface of said retainer and defining a part of said annular pocket,said ring further includes a radial sealing surface spaced from saidradial sealing surface of said retainer to further define said annularpocket, said O-ring being positionable in sealing contact with saidradial sealing surface of said ring when positioned on said outercylindrical sealing surface of said retainer and being positionable insealing contact with said inner cylindrical surface of said ring whenpositioned on said conical ramp in sealing relation to said radialsealing surface of said retainer the steps further comprisingpositioning said O-ring on said outer cylindrical surface of saidretainer in contact with said radial sealing surface of said ring whenthe pressure of the barrier gas exceed the pressure of the process fluidand positioning said O-ring on said control ramp in sealing contact withsaid radial sealing surface of said retainer and said inner cylindricalsealing surface of said ring when the pressure of the process fluidexceeds the pressure of the barrier gas.